Improve siphash performance for longer data

src/libcore/hash/sip.rs

@@ -10,6 +10,7 @@
 
 //! An implementation of SipHash 2-4.
 
+use ptr;
 use prelude::*;
 use super::Hasher;
 
@@ -31,9 +32,13 @@ pub struct SipHasher {
     k0: u64,
     k1: u64,
     length: usize, // how many bytes we've processed
+    // v0, v2 and v1, v3 show up in pairs in the algorithm,
+    // and simd implementations of SipHash will use vectors
+    // of v02 and v13. By placing them in this order in the struct,
+    // the compiler can pick up on just a few simd optimizations by itself.
     v0: u64,      // hash state
-    v1: u64,
     v2: u64,
+    v1: u64,
     v3: u64,
     tail: u64, // unprocessed bytes le
     ntail: usize,  // how many bytes in tail are valid
@@ -65,6 +70,20 @@ macro_rules! u8to64_le {
     });
 }
 
+/// Load a full u64 word from a byte stream, in LE order. Use
+/// `copy_nonoverlapping` to let the compiler generate the most efficient way
+/// to load u64 from a possibly unaligned address.
+///
+/// Unsafe because: unchecked indexing at i..i+8
+#[inline]
+unsafe fn load_u64_le(buf: &[u8], i: usize) -> u64 {
+    debug_assert!(i + 8 <= buf.len());
+    let mut data = 0u64;
+    ptr::copy_nonoverlapping(buf.get_unchecked(i),
+                             &mut data as *mut _ as *mut u8, 8);
+    data.to_le()
+}
+
 macro_rules! rotl {
     ($x:expr, $b:expr) =>
     (($x << $b) | ($x >> (64_i32.wrapping_sub($b))))
@@ -146,12 +165,11 @@ impl SipHasher {
 
         // Buffered tail is now flushed, process new input.
         let len = length - needed;
-        let end = len & (!0x7);
         let left = len & 0x7;
 
         let mut i = needed;
-        while i < end {
-            let mi = u8to64_le!(msg, i);
+        while i < len - left {
+            let mi = unsafe { load_u64_le(msg, i) };
 
             self.v3 ^= mi;
             compress!(self.v0, self.v1, self.v2, self.v3);

src/libcoretest/hash/sip.rs

@@ -7,7 +7,7 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-use test::Bencher;
+use test::{Bencher, black_box};
 
 use core::hash::{Hash, Hasher};
 use core::hash::SipHasher;
@@ -57,6 +57,12 @@ fn hash_with_keys<T: Hash>(k1: u64, k2: u64, x: &T) -> u64 {
     st.finish()
 }
 
+fn hash_bytes(x: &[u8]) -> u64 {
+    let mut s = SipHasher::default();
+    Hasher::write(&mut s, x);
+    s.finish()
+}
+
 #[test]
 #[allow(unused_must_use)]
 fn test_siphash() {
@@ -266,10 +272,88 @@ officia deserunt mollit anim id est laborum.";
     })
 }
 
+#[bench]
+fn bench_u32(b: &mut Bencher) {
+    let u = 162629500u32;
+    let u = black_box(u);
+    b.iter(|| {
+        hash(&u)
+    });
+    b.bytes = 8;
+}
+
+#[bench]
+fn bench_u32_keyed(b: &mut Bencher) {
+    let u = 162629500u32;
+    let u = black_box(u);
+    let k1 = black_box(0x1);
+    let k2 = black_box(0x2);
+    b.iter(|| {
+        hash_with_keys(k1, k2, &u)
+    });
+    b.bytes = 8;
+}
+
 #[bench]
 fn bench_u64(b: &mut Bencher) {
     let u = 16262950014981195938u64;
+    let u = black_box(u);
     b.iter(|| {
-        assert_eq!(hash(&u), 5254097107239593357);
-    })
+        hash(&u)
+    });
+    b.bytes = 8;
+}
+
+#[bench]
+fn bench_bytes_4(b: &mut Bencher) {
+    let data = black_box([b' '; 4]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 4;
+}
+
+#[bench]
+fn bench_bytes_7(b: &mut Bencher) {
+    let data = black_box([b' '; 7]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 7;
+}
+
+#[bench]
+fn bench_bytes_8(b: &mut Bencher) {
+    let data = black_box([b' '; 8]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 8;
+}
+
+#[bench]
+fn bench_bytes_a_16(b: &mut Bencher) {
+    let data = black_box([b' '; 16]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 16;
+}
+
+#[bench]
+fn bench_bytes_b_32(b: &mut Bencher) {
+    let data = black_box([b' '; 32]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 32;
+}
+
+#[bench]
+fn bench_bytes_c_128(b: &mut Bencher) {
+    let data = black_box([b' '; 128]);
+    b.iter(|| {
+        hash_bytes(&data)
+    });
+    b.bytes = 128;
 }